1. Field of Invention
The present invention relates to an induction type transducer and an electronic caliper, and in particular, an induction type transducer and an electronic caliper which are excellent in environmental durability.
2. Description of Related Art
Measuring equipment such as an electronic caliper or the like has been widely used for measuring the thickness and other physical dimensions of objects in manufacturing industries. As a main component of an electronic caliper, a transducer has been used.
Among various transducers, a capacitive coupling type transducer is generally known. In the capacitive coupling type transducer, a transmitter electrode and a reception electrode are provided on a grid (slider), and a signal electrode is provided on a scale opposed to this grid. The transmitter electrode and reception electrode on the grid are capacitively coupled with the signal electrode on the scale. A drive signal is supplied to the transmitter electrode, a detection signal generated by the reception electrode in accordance with the relative positions of the grid and scale is processed by a processing circuit, whereby the movement or position of the grid with respect to the scale is detected.
In the capacitive coupling type transducer, since it is necessary to capacitively couple the transmitter electrode and reception electrode with the signal electrode, the distance between these electrodes must be set to approximately 0.1 mm. Generally, a grid assembly is attached so as to lay across the scale in a caliper, however, in order to set the distance between the transmitter electrode and reception electrode of the grid and the signal electrode of the scale to approximately 0.1 mm as mentioned above while making smooth movements of the grid assembly and the scale possible, it becomes necessary to machine a substrate provided on the grid on which the transducer is formed.
FIG. 6 is a schematic sectional view of a related art electronic caliper using a capacitive coupling type transducer. A grid assembly 12 is attached so as to lay across a scale 10, and the grid assembly 12 slides on the scale 10 in the horizontal direction of the paper surface. The grid assembly 12 includes a substrate 14 at which the capacitive coupling type transducer is formed. The the surface of the substrate 14 is cut so as to have step 16 so that the distance between the transmitter electrode and reception electrode formed on the surface of the substrate and the signal electrode at the scale side is set to approximately 0.1 mm.
Such a capacitive coupling type transducer is suitable for use in a relatively dry and clean environment such as an inspection room or a design office. However, when such a capacitive coupling type transducer is used for dimensional measurements in an environment with a relatively high degree of pollution such as a machine shop or the like, problems arise. That is, when the transducer is used in such a polluted environment, in most cases, particulate substances or fluids such as metallic particles, polishing residue, cooling or cutting fluids exist, and if a liquid enters between the grid and scale as shown by the arrows in the figure, the liquid permeates from the step 16 of the substrate 14 into the substrate 14, damages the electrode part of the substrate and further damages the signal processing part, resulting in a detection error and measurement disablement. In addition, if metallic particles and polishing residue enter between the grid and scale, the capacitance between the signal electrode and the transmitter or reception electrode is changed, resulting in a detection error.
On the other hand, in an induction type transducer, since the relative positions are detected based on electromagnetic induction between the grid and scale, the transducer is durable for dimensional measurements in an environment with a relatively high degree of pollution.
However, even in the case where the induction type transducer is used, if a large amount of metallic particles enter between the grid and scale, the magnetic permeability between the grid and scale changes, so that the detection accuracy may lower.
Therefore, a first object of the invention is to provide an induction type transducer and an electronic caliper which are excellent in environmental durability and can be used even in an environment with a relatively high degree of pollution.
Also, a second object of the invention is to provide an electronic caliper (including equivalent measuring equipment which detects relative displacement between two members) which can detect positions with high accuracy even in an environment with a high degree of pollution regardless of the type of the transducer such as a capacitive coupling type or an induction type.
In order to achieve the first object, the induction type transducer of the invention, which outputs an electric signal in accordance with relative displacement between two members, comprises a substrate, a measuring side surface of the substrate, at which a magnetic flux generator, a magnetic flux detector, and a signal processor are formed, being made flat. The related art capacitive coupling type is not used, but the induction type transducer using magnetic induction between two members is used, whereby the coupling distance between the two members can be set to be larger than that of the capacitive coupling type. Thereby, unlike the related art example, it becomes unnecessary for the space between the members to be narrowed by providing a step at the surface of the substrate, and a liquid that has entered can be prevented from permeating into the substrate by making the surface of the substrate flat. Furthermore, in the induction type transducer, even if pollutants such as water or oil mix between the two members, the magnetic flux and magnetic non-permeability barely change, so that there is no influence on the induced voltage, and relative positions can be detected with high accuracy even in an environment with a high degree of pollution.
Herein, it is preferable that the substrate is formed by building-up a plurality of layers on a core layer. By forming the substrate of a built-up substrate, through holes penetrating the substrate are reduced, and the entrance of liquid can be more effectively prevented. It is also preferable that a sealing member is provided to seal up the surrounding of the substrate and a region at which a battery as a power supply for driving the induction type transducer is housed. The induction type transducer of the invention can be built in an electronic caliper.
Moreover, the electronic caliper of the invention, comprises a scale, a grid provided so that the grid is opposed to the scale and slidable on the scale, and a transducer for detecting relative position of the grid to the scale. In the electronic caliper, the transducer is a transducer which is magnetically coupled with the scale, and the surface of the transducer opposed to the scale is flat. By employing the magnetic coupling type, it becomes possible to set the distance between the grid and scale to be relatively wide, whereby the surface of the substrate of the grid opposed to the scale can be made flat, and even if liquids such as water, oil, or a coolant enter, its permeation into the substrate is prevented, and detection errors can be prevented.
In order to achieve the abovementioned second object, the electronic caliper of the invention comprising a scale, a grid that is opposed to the scale and slidable on the scale, and a transducer which is provided on the grid to detect the relative position of the grid to the scale, wherein wipers are provided at the end part in the sliding direction of the grid to eliminate foreign bodies on the scale. If a foreign body such as metallic particles exists on the scale, the foreign body enters inside the grid from the end part in the sliding direction of the grid, changes the physical characteristics between the transducer and scale, and lowers the detection accuracy. Therefore, by providing wipers at the end part in the sliding direction of the grid for wiping-off foreign bodies on the scale, the entrance of foreign bodies is securely prevented, and the detection accuracy can be maintained even in an environment with a high degree of pollution. In addition, since the wipers themselves slide on the scale, it is desirable that the wipers have lubricity in movement so as not to obstruct the relative movement of the grid with respect to the scale. Of course, wipers which can clean foreign bodies on the scale without being contacted with the foreign body (for example, cleaning by air blow) may be provided.
Furthermore, the electronic caliper of the invention, comprises a scale, a grid which is opposed to the scale and slidable on the scale, and a transducer which is provided on the grid to detect the relative position of the grid to the scale, wherein the surface of the scale opposed to the grid is coated with a protective film. As a protective film, by applying fluorine coating on the surface of the scale, adhesion of foreign bodies such as metallic particles onto the surface of the scale is prevented, whereby the entrance of foreign bodies between the transducer and scale can be prevented. Furthermore, by fluorine-coating, the scale surface is effectively protected from acids and alkalis, so that deterioration of the scale can also be prevented.
Furthermore, the electronic caliper of the invention comprises a scale, a grid which is opposed to the scale and slidable on the scale, and a transducer which is provided on the grid to detect the relative position of the grid to the scale, wherein wipers are provided at the end part in the sliding direction of the grid to eliminate foreign bodies on the scale, and a protective film is provided on the surface of the scale opposed to the grid. As a protective film, for example, by applying fluorine-coating on the scale surface, adhesion of metallic particles and dust is prevented, and if they adhere to the scale, they are wiped off the wipers, so that the entrance of foreign bodies between the grid and scale can be securely prevented, and the detection accuracy can be maintained. Also, the lubricity and wear resistance of the scale surface can be improved by fluorine-coating, and the operation of the wipers can be made smoother. Furthermore, by fluorine-coating, a wet-proofing property is generated so as to repel water or the like, and for example, in the case where a capacitive coupling type transducer is used, operation failure can be effectively prevented.